The present invention relates to a screen-printable paste for producing a porous polymer membrane which can be used in electrochemical sensors, especially in electrochemical biosensors, for integrated preparation of, in particular, whole blood samples.
Biosensors are already in use in a large number of diagnostic methods, for example in the determination of the concentration of various factors in body fluids such as blood. The aim in this connection is to have sensors which require no elaborate processing of the (blood) sample but provide a rapid result simply by applying the body fluid to a test strip. This entail a specific biochemical reaction taking place, such as, for example, the enzymatic conversion of the component to be determined, which then brings about an electron transfer between different electrodes (working and reference electrodes), and this can be determined quantitatively.
The disadvantage of most or the known electrochemical biosensors is that, on application of the blood to the region provided therefor on the test strip, the biochemical reaction which takes place is influenced by other constituents present in the blood, especially the red blood corpuscles (erythrocytes). Thus, for example, when the values of the hematocrit (=volume of the erythrocytes as a proportion of the total amount of blood in vol.wt. %) are high, the value measured for glucose using conventional blood glucose sensors is lower than the actual value. This adverse affect arises from the fact that the erythrocytes influence, through adsorption onto the reactive layer of the biosensor, the diffusion of glucose into the latter and to the electrode and reduce the measured signal.
To solve this problem, various membranes which are put on top of the enzyme layer, which is disposed on the electrodes, of the test strip in order to keep the erythrocytes away from this layer have been proposed.
Thus, for example, U.S. Pat. No. 5,658,444 describes an erythrocyte exclusion membrane for a sensor, which consists of a water-insoluble, hydrophobic polymer, of a water-soluble hydrophilic polymer and of an erythrocyte aggregating agent and is produced by spraying onto the surface of the test strip.
One disadvantage of this membrane is that the membrane pore diameter varies as a function of the spraying distance and spray pressure. In addition, the spraying on of the membrane during production of the rest strip means an additional operation which is different from the production of the remainder of the test strip and is therefore elaborate, which makes the production process complicated and thus costly.
It is therefore an object of the present invention to provide a paste for producing a porous membrane which does not have the disadvantages mentioned since it can be applied during the biosensor production process by a method which fits in with the remaining procedure and is therefore cost-effective, and provides a membrane of constant pore size.
This object is achieved by a paste for a porous polymer membrane as claimed in claim 1. Advantageous developments are evident from claims 2 to 18.